AFR problem using Thunder Monster baffles

[AzFAL]

I did a baseline dyno run on my 95” build after having installed some Thunder Monster baffles in my V&H Bigshot staggered pipes. I must say I’m shocked & amazed at the AFR & the rich condition dip between about 2800-3800 RPMs. Not at all what I expected, reason being is that I don’t feel it in the seat of the pants.

My set-up: 95”, Dewey’s Pro-street heads, 37g gear drive cams, Wiseco flat-top pistons, 44cv carb re-worked by HDWrench, SE 6200 RPM ignition & the BSS pipes.

Posted are three dyno charts:
The 1st chart from Desert Custom Cycles was done in May. It shows 93.21 HP/ 99.62 TQ & a lean AFR with some rich condition dips at lower RPMs. Also written on it is the AFR at a couple different cruising speeds. This run was done w/ stock baffles & carb jetted with a 48 slow/200 main jets.

2nd chart was done at the another shop as we richened up the AFR by going to a 220 main jet & we tried to flatten out the rich cond. dips. Due to time constraints & such we weren’t able to finish addressing the rich cond. dips. We ended up w/ 95.6 HP/ 103.1 TQ.

3rd chart was done at Desert Custom again on Sept 1st. The blue lines are actually copies of the 1st run back in May. Everything is the same as the run at the other shop (2nd chart) except for the Thunder Monster baffles installed. You can see from the red lines (Sept. 1st run) that I lost a bit on TQ & gained a bit on HP (96.08 HP/ 101.71 TQ) with the TM baffles. Not that big of deal but the AFR rich cond. dips are at or below 10.

What I don’t understand is how I can have such severe rich cond. dips at full throttle but at the cruising speeds written on the 3rd chart I’m fine. Notice that at 45 MPH in 4th gear, which is about, 2500rpms my AFR is 14-14.3 & at 75 mph in 5th gear I’m at 13.5 AFR, right where I should be.

I called Big City Thunder & talked to Jim. He said his product is not the problem but that if there were any problems inherent in my build that using his baffles would tend to amplify those problems & make them more apparent. Alright, it does appear that what he’s saying has some truth to it since I already had rich dips & now with the TMs they’re even richer dips. He thought I was over carbed for my build, though Dewey & HDWrecnch both said the 44cv was a good carb for my build. He thought I should go with a 42mm carb or try a dynojet/Thunderslide kit.

What’s wierd is before I put in the TMs I could really feel my rich AFR dips & after putting in the TMs it feels much smoother & the bike still runs like a maniac. I have to admit the TMs definitiley wake these pipes up. They sound awesome.

Now after all that typing (whew!), any suggestions on how to get rid of those AFR rich dips? I could put back the stock baffles, but I’ve still got the AFR dips.

Why doesn’t Desert Customs #’s line up at the proper HP & TQ lines on the graph?

Any help is much appreciated.

[HDMD88]

Originally Posted by AzFAL

I did a baseline dyno run on my 95” build after having installed some Thunder Monster baffles in my V&H Bigshot staggered pipes. I must say I’m shocked & amazed at the AFR & the rich condition dip between about 2800-3800 RPMs. Not at all what I expected, reason being is that I don’t feel it in the seat of the pants.

My set-up: 95”, Dewey’s Pro-street heads, 37g gear drive cams, Wiseco flat-top pistons, 44cv carb re-worked by HDWrench, SE 6200 RPM ignition & the BSS pipes.

Posted are three dyno charts:
The 1st chart from Desert Custom Cycles was done in May. It shows 93.21 HP/ 99.62 TQ & a lean AFR with some rich condition dips at lower RPMs. Also written on it is the AFR at a couple different cruising speeds. This run was done w/ stock baffles & carb jetted with a 48 slow/200 main jets.

2nd chart was done at the another shop as we richened up the AFR by going to a 220 main jet & we tried to flatten out the rich cond. dips. Due to time constraints & such we weren’t able to finish addressing the rich cond. dips. We ended up w/ 95.6 HP/ 103.1 TQ.

3rd chart was done at Desert Custom again on Sept 1st. The blue lines are actually copies of the 1st run back in May. Everything is the same as the run at the other shop (2nd chart) except for the Thunder Monster baffles installed. You can see from the red lines (Sept. 1st run) that I lost a bit on TQ & gained a bit on HP (96.08 HP/ 101.71 TQ) with the TM baffles. Not that big of deal but the AFR rich cond. dips are at or below 10.

What I don’t understand is how I can have such severe rich cond. dips at full throttle but at the cruising speeds written on the 3rd chart I’m fine. Notice that at 45 MPH in 4th gear, which is about, 2500rpms my AFR is 14-14.3 & at 75 mph in 5th gear I’m at 13.5 AFR, right where I should be.

I called Big City Thunder & talked to Jim. He said his product is not the problem but that if there were any problems inherent in my build that using his baffles would tend to amplify those problems & make them more apparent. Alright, it does appear that what he’s saying has some truth to it since I already had rich dips & now with the TMs they’re even richer dips. He thought I was over carbed for my build, though Dewey & HDWrecnch both said the 44cv was a good carb for my build. He thought I should go with a 42mm carb or try a dynojet/Thunderslide kit.

What’s wierd is before I put in the TMs I could really feel my rich AFR dips & after putting in the TMs it feels much smoother & the bike still runs like a maniac. I have to admit the TMs definitiley wake these pipes up. They sound awesome.

Now after all that typing (whew!), any suggestions on how to get rid of those AFR rich dips? I could put back the stock baffles, but I’ve still got the AFR dips.

Why doesn’t Desert Customs #’s line up at the proper HP & TQ lines on the graph?

Any help is much appreciated.

Dave the AFR tester reads the raw fuel in your pipe....the V&H big shot pipes are one of the worst pipes you can have for performance bar none. When you installed the TM baffle it probably got rid of the dip in the tq and hp line but the pipe is too large of a diameter and too short to work for the diameter they are. Its VERY difficult to tune a carb with pipes like those. This isn't a rich dip this is a scavaging problem from the pipes. You can jet till the cows come home andnever get that area to perform well. It has to do with cam overlap intake velocity and your pipes...they don't work as a package. This is why it is so important to use a good proven pipe for performance instead of what looks good to you because 99% of the time the two don't mix. I explained in a thread aboutthe exhaust scavaging and how it effects you power awhile back...its good info on this very subject. The only way to fix this problem is to off the BIG SHOTS pipes. The dyno is reading an AFR that you arent keeping in the combustion chamber....do to bad scavaging.

[AzFAL]

I hear what you're saying Doc. New pipes right now aren't an option. (Maybe Chistmas.) Actually according to the 3rd dyno run I've got a broader & more of a torque dip with the TMs in, but I don't feel it like I did with the stock bafffles.

How come the AFR shows the over scavenging in the 2800-3800 RPM range but at the cruising speeds written to the right on the 3rd chart my AFR looks good?

Is the over-scavenging causing my AFR to go down to 10 going to hurt my engine or anything?

When & if I'm able to get some 2-1 pipes, which from your previous posts looks like the Pro-pipe is your favorite, how much do you estimate it will boost my numbers?

Thanks

[HDMD88]

Originally Posted by AzFAL

I hear what you're saying Doc. New pipes right now aren't an option. (Maybe Chistmas.) Actually according to the 3rd dyno run I've got a broader & more of a torque dip with the TMs in, but I don't feel it like I did with the stock bafffles.

How come the AFR shows the over scavenging in the 2800-3800 RPM range but at the cruising speeds written to the right on the 3rd chart my AFR looks good?

Is the over-scavenging causing my AFR to go down to 10 going to hurt my engine or anything?

When & if I'm able to get some 2-1 pipes, which from your previous posts looks like the Pro-pipe is your favorite, how much do you estimate it will boost my numbers?

Thanks

The large Dia pipe with the TH does crazy things...not ever build is effective the same. I don't think your AFR looks all that great in any of the graphs. I can read the middle graphs the other two the shop was more proud of their name than the graphs cause there wasn't any room on the page for the graphs. Those small sections they have are reduclious, you needto see the curves in the lines not just a line going across the page.
You can expect to see a 5% to 8% change for the good with a Pro Pipe, and a much better fuel line.